1. Field of the Disclosed Subject Matter
The disclosed subject matter relates to roofing material, and in particular to roofing shingles, having a transition zone which imparts improved characteristics, such as impact resistance to damage from hail, ice, and other debris.
2. Description of the Related Art
Roofing material, such as shingles, has a front upper surface, at least a portion of which is intended to be exposed to weather, and a back lower surface facing in the direction opposite to the upper surface. The shingles are installed overlapping such that the headlap of the front upper surface of a shingle is disposed underneath the exposed portion of a shingle thereabove. Traditionally, the back, non-weather-exposed surface of roofing material has been covered with finely ground mineral material (“fines”) so that the asphalt backing does not adhere to contiguous roofing material when packaged for transport and storage. Such finely divided materials include mica flakes, copper slag, coal slag, sand, talc and silica dust. The front exposed surface of roofing material can also include the fines in certain applications.
In many areas, the roofing materials on buildings, particularly the shingles on residential dwellings, are damaged by hail, ice, and other debris. The damage is caused by the impact of external forces such as hail stones striking shingles resulting in visible cracking, tearing, snapping or imperceptible damage to the shingles' structure which can render the shingles less resistant to the elements of wind, rain, snow and ice. Frequently, such damage requires the costly replacement of roofing materials to prevent the elements from entering into the building.
There are several solutions in the art which have attempted to improve the impact resistance of shingles. U.S. Pat. No. 6,341,462 B2, to Kiik et al., the subject matter of which is herein incorporated by reference, discloses a roofing material with improved resistance to damage by hail having an energy-absorbing backing layer adhered to its lower surface. The backing layer of U.S. Pat. No. 6,341,462 comprises fiber and binding components with a combined weight ranging between 0.5 and 5 lbs. per square (100 square feet) of shingle material such that the exposed portion of a shingle made according to U.S. Pat. No. 6,341,462 appears more substantial and is, indeed, visibly thicker prior to application than products made without the backing layer. U.S. Pat. No. 7,851,051, to DeJarnette et al., the subject matter of which is herein incorporated by reference, discloses a roofing material with improved resistance to damage by hail having an upper and lower surface in which a thin layer comprising re-melted polypropylene or other suitable plastic is adhered to at least a portion of its lower surface.
As most shingles are installed overlapping with adjacent shingles, the top edge of an underlying shingle ends at an approximate center region of an overlying shingle. This top edge of the underlying shingle can cause further stresses to the overlying shingle when impact forces, such as hail, strike this approximate center region. The edge of the underlying shingle can create a relatively sharp drop off ledge which can impose additional stresses on the overlying shingle. Thus, there remains a continued need for an efficient and economic system for impact resistance for roofing materials, such as shingles. The presently disclosed subject matter satisfies these and other needs.